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Two-dimensional normal-state quantum oscillations in a superconducting heterostructure
Kozuka, Y.,Kim, M.,Bell, C.,Kim, B. G.,Hikita, Y.,Hwang, H. Y. Macmillan Publishers Limited. All rights reserved 2009 Nature Vol.462 No.7272
Semiconductor heterostructures provide an ideal platform for studying high-mobility, low-density electrons in reduced dimensions. The realization of superconductivity in heavily doped diamond, silicon, silicon carbide and germanium suggests that Cooper pairs eventually may be directly incorporated in semiconductor heterostructures, but these newly discovered superconductors are currently limited by their extremely large electronic disorder. Similarly, the electron mean free path in low-dimensional superconducting thin films is usually limited by interface scattering, in single-crystal or polycrystalline samples, or atomic-scale disorder, in amorphous materials, confining these examples to the extreme ‘dirty limit’. Here we report the fabrication of a high-quality superconducting layer within a thin-film heterostructure based on SrTiO<SUB>3</SUB> (the first known superconducting semiconductor). By selectively doping a narrow region of SrTiO<SUB>3</SUB> with the electron-donor niobium, we form a superconductor that is two-dimensional, as probed by the anisotropy of the upper critical magnetic field. Unlike in previous examples, however, the electron mobility is high enough that the normal-state resistance exhibits Shubnikov–de Haas oscillations that scale with the perpendicular field, indicating two-dimensional states. These results suggest that delta-doped SrTiO<SUB>3</SUB> provides a model system in which to explore the quantum transport and interplay of both superconducting and normal electrons. They also demonstrate that high-quality complex oxide heterostructures can maintain electron coherence on the macroscopic scales probed by transport, as well as on the microscopic scales demonstrated previously.
Kyuichi Yasui,Teruyuki Kozuka,Masaki Yasuoka,Kazumi Kato 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.10
There are two major categories in a thermoacoustic prime-mover. One is the traveling-wave type and the other is the standing-wave type. A simple analytical model of a standing-wave thermoacoustic prime-mover is proposed at relatively low heat-flux for a stack much shorter than the acoustic wavelength, which approximately describes the Brayton cycle. Numerical simulations of Rott’s equations have revealed that the work flow (acoustic power) increases by increasing of the amplitude of the particle velocity (|U|) for the traveling-wave type and by increasing cos for the standing-wave type, where is the phase difference between the particle velocity and the acoustic pressure. In other words, the standing-wave type is a phase-dominant type while the traveling-wave type is an amplitude-dominant one. The ratio of the absolute value of the traveling-wave component (|U|cos) to that of the standing-wave component (|U|sin) of any thermoacoustic engine roughly equals the ratio of the absolute value of the increasing rate of |U| to that of cos. The different mechanism between the traveling-wave and the standing-wave type is discussed regarding the dependence of the energy efficiency on the acoustic impedance of a stack as well as that on !, where ! is the angular frequency of an acoustic wave and is the thermal relaxation time. While the energy efficiency of the traveling-wave type at the optimal ! is much higher than that of the standing-wave type, the energy efficiency of the standing-wave type is higher than that of the traveling-wave type at much higher ! under a fixed temperature difference between the cold and the hot ends of the stack.
Kim, Gyung-Tae,Fujioka, Shozo,Kozuka, Toshiaki,Tax, Frans E.,Takatsuto, Suguru,Yoshida, Shigeo,Tsukaya, Hirokazu Blackwell Science Ltd 2005 The Plant journal Vol.41 No.5
<P>Summary</P><P>Brassinosteroids (BRs) are plant hormones that are essential for a wide range of developmental processes in plants. Many of the genes responsible for the early reactions in the biosynthesis of BRs have recently been identified. However, several genes for enzymes that catalyze late steps in the biosynthesis pathways of BRs remain to be identified, and only a few genes responsible for the reactions that produce bioactive BRs have been identified. We found that the <I>ROTUNDIFOLIA3</I> (<I>ROT3</I>) gene, encoding the enzyme CYP90C1, which was specifically involved in the regulation of leaf length in <I>Arabidopsis thaliana</I>, was required for the late steps in the BR biosynthesis pathway. ROT3 appears to be required for the conversion of typhasterol to castasterone, an activation step in the BR pathway. We also analyzed the gene most closely related to <I>ROT3</I>, <I>CYP90D1</I>, and found that double mutants for <I>ROT3</I> and <I>CYP90D1</I> had a severe dwarf phenotype, whereas <I>cyp90d1</I> single knockout mutants did not. BR profiling in these mutants revealed that CYP90D1 was also involved in BR biosynthesis pathways. <I>ROT3</I> and <I>CYP90D1</I> were expressed differentially in leaves of <I>A. thaliana</I>, and the mutants for these two genes differed in their defects in elongation of hypocotyls under light conditions. The expression of <I>CYP90D1</I> was strongly induced in leaf petioles in the dark. The results of the present study provide evidence that the two cytochrome P450s, CYP90C1 and CYP90D1, play distinct roles in organ-specific environmental regulation of the biosynthesis of BRs.</P>
Public Investment and Stock Price Returns: The Case of Japan
Tomomi Miyazaki,Kazuki Hiraga,Masafumi Kozuka 한국재정학회 2017 한국재정학회 학술대회 논문집 Vol.2017 No.-
This research examines the effects of public investment on stock price returns using the Japan’s cross-industry data. To do so, we calculate the impulse response function by local projection method. The empirical results show that public investment has a positive impact on stock price returns. We observe this mainly for manufacturing industries both in quarterly and annual data. However, the policy effects after the 1990s was not necessarily large enough to stimulate the economy. Our empirical evidence on the post high-growth era in Japan suggests that public investment has been partly useful to support the revitalization of stock market.
MRI Appearance of Prostatic Stromal Sarcoma in a Young Adult
Tsutomu Tamada,Teruki Sone,Yoshiyuki Miyaji,Yuji Kozuka,Katsuyoshi Ito 대한영상의학회 2011 Korean Journal of Radiology Vol.12 No.4
Prostatic stromal sarcoma (PSS) is quite rare. Herein, we describe magnetic resonance imaging (MRI) features of a PSS identified in a 26-year-old man with dysuria and hematuria. MRI clearly depicted the extent and multinodular appearance of the tumor, which was mainly located in the central zone of the prostate. The tumor appeared as a heterogeneously signal-hyperintense mass with a pseudocapsule on T2-weighted imaging. Contrast-enhanced T1-weighted MRI showed necrotic portions in the gradually enhanced solid mass, and diffusion-weighted imaging permitted the accurate assessment of the local extent of the tumor. Thus, the appearance on MRI was quite different from that of adenocarcinoma of the prostate.